This invention relates to electroconductive coating compositions and to coated articles employing them.
In the manufacture of many articles employing nonconductive substrates as a component part of such articles, it is often desirable to reduce the surface electrical resistivity of the nonconductive substrate to a value below 10.sup.14 ohms at 10 percent relative humidity. For example, paper which has been rendered electroconductive may be used to distribute electrical stresses in various insulating products. Also, the support normally used in electrographic, electrophotographic, electrostatic and other nonimpact printing processes is conductive or is coated with a conductive layer, and as such plays a role in the formation of the image or the record.
In electrophotographic recording elements, a photoconductive layer stands in contact with an electroconductive layer or sheet, the latter being present to enable charging of the photoconductive layer and to dissipate the electrostatic charges from the areas of the photoconductive layer undergoing an exposure to light rays. As the photoconductive or photoresponsive material, there is most often used a specially treated zinc oxide coating. Where light strikes portions of the paper treated with such a light sensitive material, the electrical charge is dissipated in those areas exposed to light. As a result, there is left a pattern of charged and uncharged areas. The charged area will then be effective to attract an oppositely charged powder, or other usually particulated image forming material. Such a powder will not be attracted to the light affected discharge areas, and the powder may thus be deposited on the paper in a pattern which corresponds with the charged areas. Generally, such an image forming material may then be fused, or otherwise treated, on the paper to make the image permanent. Such an image forming material is often a wax coated finely divided carbon black which will fuse when heated on the paper.
While other nonimpact printing processes differ from the above in that the images are created by electrical dissipation of the static charge in nonimage areas, all require as a common characteristic an electrically conductive substrate such as an electroconductive paper.
Conventionally, paper and other nonconductive substrates have been rendered electroconductive by coating same with various electroconductive additives such as water-soluble quaternary ammonium polymers as exemplified in Silvernail et al., U.S. Pat. No. 3,011,918, Booth et al., U.S. Pat. No. 3,544,318, Cavagna et al., U.S. Pat. No. 3,479,215, and Rogers et al., U.S. Pat. No. 3,320,317.
In the production of electroconductive paper, the base substrate, i.e., the raw paper stock, is generally precoated with a composition of binder and pigment. Subsequently, the electroconductive resin is applied to the precoated paper, usually as an aqueous formulation of the resin, a pigment and oftentimes a binder. While the use of a binder is desirable and often necessary to provide coating strength and organic solvent resistance as well as a more economical material, the presence of the binder significantly reduces the electroconductivity of the resultant coating. Furthermore, some binders and electroconductive resins are so incompatible that stable coating compositions cannot be suitably prepared.
Therefore, it would be highly desirable to provide a stable electroconductive coating composition containing a significant amount of binder wherein the surface electrical resistivity and solvent resistance of the resultant coating are not materially impaired.